So, what really irks you is that those with traditional IRAs might "get away with something" while those with ROTH IRAs would have already paid taxes on what they donated. While that may be a grievance, it is hardly a huge problem or cause to call the Fair Tax a "double taxation fraud". Using your reasoning, we should scrap all possibly good things if they don't first level the playing field to ensure some folks don't benefit because of existing conditions, no matter how much good the new ideas might effect. Sounds real similar to the Dims always wanting to lay more and more taxes on the "rich" because they have more than the poor. How dare someone have more and/or benefit more, even in the short run....
Roths are like nothing in comparison with the total pool of already taxed money - besides Roths it includes savings AND the capital cost basis of every taxable investment in the country. And the double taxation fraud would apply to all of these, not merely to Roths. So it's a bit more than a "grievance".